Erin Ouslander, UMBC When tears are removed digitally from photograph of a crying face, the expression seems not only less sad but also emotionally ambivalent. A neuroscientist says that the “tear effect” represents an evolutionary breakthrough for humans. [via nytimes]

What’s the use of crying when you’re sad? Other animals shed tears, but humans may be unique in shedding tears of grief, and Robert Provine says that he knows why: to send a signal.

“Emotional tears are a breakthrough in the evolution of humans as a social species,” says Dr. Provine, a neuroscientist at the University of Maryland, Baltimore County. Writing in Evolutionary Psychology (pdf), he reports the first experimental demonstration of what he calls the “tear effect.” The subjects in the experiment were asked to rate the sadness of photographs of people crying, but in some of the photos the tears were digitally removed. (The experiment used actual photographs of people, not the cartoon images shown above.) When the tears were removed, the people were rated less sad, and their faces were often mistakenly interpreted as expressions of awe, puzzlement or concern. Dr. Provine concludes:

Emotional tears resolve ambiguity and add meaning to the neuromuscular instrument of facial expression, what we term the tear effect. Tears are not a benign secretory correlate of sadness or other emotional state. Emotional tears may be exclusively human and, unlike associated vocal crying, do not develop until a few months after birth. The emergence of emotional tearing during evolution and development is a significant but neglected advance in human social behavior that taps an already established secretory process involving the eye, a primary target of visual attention.

Dr. Provine says that so little is known about why adults cry that there are lots more questions to answer. “Do tears, for example, make a person appear more needy, helpless, frustrated, or powerless, as well as sadder?” he asks. “Do tears amplify a perceived emotional expression, add a unique message, or contribute a subtle nuance interpreted as sincerity or wistfulness?”

You’re welcome to offer answers, or any thoughts on what may be another unique human trait: fake tears of sadness. (As far I know, those crocodile tears are not shed by crocodiles or any other animals.) Dr. Provine says he’d like to test the effect of digitally adding tears to faces. How widespread is the ability of people to cry fake tears, and how effective is that signal of sadness?